An input signal (if you want gain), changes the applied voltage between Base and Emitter.
The emitter voltage won't change in this circuit because it's grounded. Therefore the input must be the Base.
The only way left to get an output is the Collector and typically the signal is the collector voltage referenced to Ground.
Since the Emitter is used as the reference for both input and output, It is called a common-Emitter configuration.

If you have a circuit with the Base grounded, the signal input is to the Emitter, and output is from the Collector, you have a common-Base configuration.

Your right Tom, I would guess Rb is a bias Resistor, The Emitter is tied to ground and the Collector to Vcc..Now lets assume the input is tied to the Base and the output is picked off the Rc by convention..If we do, then I would guess it is a CE...

To the OP.. The element that has no input or output and typically tied to grd is the "common", hence, Common Emitter, Base, or Collector..

Again, since the emitter is grounded and the collector has a Rc or load resistor and guessing the base is being fed a bias voltage from the collector, the only element with no in/output would assumably be the emitter..Once again, with a little supposition, this could be a common emitter configuration since the emitter is common to the input and output, and is grounded.

Once again, like Tom said..without the in/output being showed we both are kinda' guessing here saranga...

An input signal (if you want gain), changes the applied voltage between Base and Emitter.
The emitter voltage won't change in this circuit because it's grounded. Therefore the input must be the Base.
The only way left to get an output is the Collector and typically the signal is the collector voltage referenced to Ground.
Since the Emitter is used as the reference for both input and output, It is called a common-Emitter configuration.

If you have a circuit with the Base grounded, the signal input is to the Emitter, and output is from the Collector, you have a common-Base configuration.

Your right Tom, I would guess Rb is a bias Resistor, The Emitter is tied to ground and the Collector to Vcc..Now lets assume the input is tied to the Base and the output is picked off the Rc by convention..If we do, then I would guess it is a CE...

To the OP.. The element that has no input or output and typically tied to grd is the "common", hence, Common Emitter, Base, or Collector..

Again, since the emitter is grounded and the collector has a Rc or load resistor and guessing the base is being fed a bias voltage from the collector, the only element with no in/output would assumably be the emitter..Once again, with a little supposition, this could be a common emitter configuration since the emitter is common to the input and output, and is grounded.

Once again, like Tom said..without the in/output being showed we both are kinda' guessing here saranga...

Your right Tom, I would guess Rb is a bias Resistor, The Emitter is tied to ground and the Collector to Vcc..Now lets assume the input is tied to the Base and the output is picked off the Rc by convention..If we do, then I would guess it is a CE...

To the OP.. The element that has no input or output and typically tied to grd is the "common", hence, Common Emitter, Base, or Collector..

Again, since the emitter is grounded and the collector has a Rc or load resistor and guessing the base is being fed a bias voltage from the collector, the only element with no in/output would assumably be the emitter..Once again, with a little supposition, this could be a common emitter configuration since the emitter is common to the input and output, and is grounded.

Once again, like Tom said..without the in/output being showed we both are kinda' guessing here saranga...